The present invention relates generally to a paper feed apparatus. More particularly, the invention relates to a paper feed apparatus of a bottom discharge type having an automatic paper feed apparatus for use in image reading system where paper sheet separating performance for separating paper sheets being fed, such as manuscripts and cut sheets, can be enhanced, and operability can be improved by eliminating the need for special preliminary operations when setting paper sheets.
Most image reading devices for reading a large amount of manuscripts transported automatically have an automatic paper feed apparatus comprising a paper pickup mechanism for causing a plurality of paper sheets stacked on a chute to move to a predetermined standby position, a separating mechanism for separating and picking up and transporting the paper sheets onto the standby position one by one, a feed mechanism for transporting the paper sheet, and a paper discharge mechanism for discharging the paper sheets after image reading to a stacker or outside the paper feed apparatus. In recent years, the aforementioned automatic paper feed apparatus is controlled by a microprocessor in most cases.
FIG. 27 is a diagram illustrating a prior-art paper feeding apparatus. In the figure, a pickup roller 72 and a separating roller 73 are disposed so that both the rollers 72 and 73 can be rotated in the same direction via a gear 83, and also can be rotated in conjunction with a feed roller 74 via a gear 79, The pickup roller 72 is caused to make a sliding contact with a pressure arm 81, and the separating roller 73 is caused to make a sliding contact with a separating pad 80, respectively. A gate 84 is provided in a paper feed path between the pickup roller 72 and the separating roller 73.
The pressure arm 81, which is typically made of a spring member, is provided to ensure the transportation of a paper sheet set on the chute 71. An end of the pressure arm 81 is fixedly fitted to a (not shown), and the other end thereof is forced onto the paper sheet by a pushing force in the direction of the pickup roller 72. The pushing force, together with force between the pickup roller and the paper, acts to take up and transport the paper sheet to the separating roller 73.
The gate 84 is used to provide a clearance in the direction of paper thickness in the paper feed path so that a few sheets of paper can pass, and is disposed at an acutely inclined position with respect to the direction of paper entry into the paper feed path to ensure positive paper transport.
A one-way clutch is provided on each of the shafts of the pickup roller 72, the separating roller 73 and a discharge roller 75 so that the separating roller 73 can rotate only in a counterclockwise direction, and the discharge roller 75 only in a clockwise direction (paper feed direction). A sensor 82 for sensing the leading edge of paper is provided on the downstream side of the paper feed path near the separating roller 73. A sensor 85 for sensing the leading/trailing end of paper is also provided on the downstream side of the paper feed path near the feed roller 74.
In the aforementioned automatic paper feed apparatus, as a pulley 76 of a motor (not shown) is rotated in a counterclockwise direction, the feed roller 74 is rotated in a counterclockwise direction by a belt 77, that is, in the direction opposite to the direction of paper feed. The discharge roller 75 remains stationary even when the belt 77 is rotated. The pickup roller 72 and the separating roller 73 are rotated in a counterclockwise direction by gears 79 and 83. Consequently, paper sheets (not shown) stacked on the chute 71 are taken up one by one by the pickup roller 72, and transported toward the separating roller 73. Should multiple paper sheets be erroneously taken up en bloc, only one paper sheet that is in close contact with the pickup and separating rollers 72 and 73 is transported toward the feed roller 74 by the blocking action of the gate 84 and the separating pad 80. Thus, what is called double feeding can be prevented.
Next, even when the leading edge of the transported paper sheet reaches the feed roller 74, the paper sheet is not immediately fed to the feed roller 74, staying there for a while because the feed roller 74 is, rotated counterclockwise, or in the direction opposite to the paper feed direction. Thus, the edge of the paper sheet is aligned during the period. The retention time of the paper sheet is controlled based on a predetermined number of pulses or a predetermined time after the sensor 82 has detected the leading edge of the paper sheet. After the lapse of a predetermined retention time, the motor (not shown) is reversed to cause the pulley 76 to rotate clockwise. As a result, the feed and discharge rollers 74 and 75 are also caused to rotate clockwise by the belt 77, with the paper sheet transported to the reading mechanism 78 by the feed roller 74. Immediately before it, the leading edge of the paper sheet is detected by the sensor 85, and reading is initiated by a signal generated by the sensor 85. As the sensor 85 detects the trailing end of paper, reading is terminated and the paper sheet is discharged onto a stacker (not shown) by the discharge roller 75.
In the aforementioned automatic paper feed apparatus where multiple sheets of paper 90 as shown in FIG. 28(a) are set on the chute 71, a preparatory operation is required to form the leading edges of the paper sheets into a knife edge 91, or cause the leading edges of the paper sheets to feather, as shown in FIG. 28 (b), to ensure that paper sheets are taken up onto the separating roller 73 smoothly and positively.
As described above, the paper feed apparatus of the prior art has the following problems:
(1) Since the gate for providing a clearance in the paper thickness direction in the paper feed path is disposed at an acutely inclined position to the paper entry direction, the resulting vertical component force produces a force contributing to unwanted multiple-sheet feeding, lowering the paper separating performance.
(2) When setting multiple sheets of paper on the chute, a preparatory operation is needed to form the leading edges of paper sheets into a knife edge (or cause the front face of the paper stack to feather). This preparatory operation, however, is so complex that the operator is often induced to neglect it. This may result in failure to ensure smooth paper feeding.
(3) As described above, the separating roller is disposed between the pickup and feed rollers, and the pickup roller is caused to make sliding contact with the pressure arm, and the separating roller with the separating pad. All these arrangements have made the transport mechanism of the prior-art paper feed apparatus an oversized unit.
It has been required that the aforementioned problems in the prior-art paper feed apparatus be solved, and that all paper sheets, large or small, be properly supplied in the paper feed apparatus. That is, pickup errors that could happen when handling a large amount of paper sheets, or multiple-sheet feeding associated with a small number of paper sheets, or paper jams associated with thin paper sheets must be prevented.
It is an object of this invention to provide a paper feed apparatus that can feed paper sheets properly.
To overcome the above-mentioned problems, a paper feed apparatus embodying the present invention employs the following means:
In a paper feed apparatus having a pickup mechanism to pick up a plurality of sheets of paper stacked on a chute one by one from the bottom, and carrying the paper sheet to a predetermined preparatory position;
a gate disposed facing the pickup roller almost vertically with respect to the direction of paper entry to form a predetermined clearance, a paper-sheet separating pad making sliding contact with the pickup roller to pick up the paper sheets placed on the preparatory position one by one, and a pickup arm that is moved upward when setting paper sheets, and moved downward when feeding the paper sheets, to push from above the paper sheets stacked on the chute at the paper feeding port are provided;
the pickup arm is driven by a planetary gear-based clutch mechanism and a motor for feeding paper sheets that is used in common as a drive source for the pickup arm in such a manner that the pickup arm is moved downward as the forward rotation of the motor disengages the planetary gear from a drive power transmission system, and the pickup arm is moved upward as the reverse rotation of the motor engages the planetary gear with the drive power transmission system; and
the pickup arm, when brought into free state as the planetary gear are disengaged from the drive power transmission system, pushing the paper sheets with a pushing force that increases with increases in the number of paper sheets stacked on the chute.
By employing the above means, the paper feed apparatus embodying the present invention can make the whole unit compact in size and prevent multiple-sheet feeding force from being generated in a gate mechanism disposed almost vertically with respect to the paper entry direction, thereby improving the paper separating performance. Furthermore, paper-sheet edge aligning operation can be eliminated when a plurality of paper sheets are set on the chute by maintaining positive paper-sheet pickup performance. Furthermore, paper sheets can be pushed with an optimum pushing force by the pickup arm since a small pushing force is exerted on the paper sheets when a small number of paper sheets are stacked on the chute, while a large pushing force is applied when a large number of paper sheets are stacked on the chute. As a result, the rate of successful paper pickup against user""s paper-sheet setting can be improved even when thin paper sheets are used, and power consumption in the motor can be reduced.